Ignition system for internal combustion engine

ABSTRACT

The disclosed ingition system includes a monostable multivibrator passing into its semistable state each time the associated engine is to be ignited to put a normally conducting switching transistor in its nonconducting state. This causes the interruption of a current flowing through an ignition coil to generate an ignition voltage across it. In the monostable multivibrator a capacitor is serially connected to a resistor high in magnitude of resistance to increase a time constant for charging and a semiconductor diode is connected across the resistor to decrease a time constant for discharging.

ilnited tates Patent Saita Feb. 12, 1974 '[54] IGNITION SYSTEM FORINTERNAL 3,554,169 1/1971 W:1hl 123/148 F. COMBUSTION ENGINE 3,473,06110/1969 Sochncr 123/1481".

[75] Inventor: Toshikazu Saita, Himeji, Japan Primary ExaminerLaurence.M. fioodridge [73] Assignee: Mitsubishi Denki Kabushiki Kaisha,Assis nt Examiner-Cort Flint Tokyo, Ja an Attorney, Agent, orFirm--Robert E. Burns; Emman- IJ. Lob t 221 Filed: May 26, 1971 a o [21]App]. No.: 146,934 [57] ABSTRACT The disclosed ingition system includesa monostable [30] Foreign Application Priorit Dat multivibrator passinginto its semistable state each June 3, 1970 Japan 45/54605 time theassociated ergine is be ignited Put a normally conducting switchingtransistor in its non- [52] Cl. 123/148 E, 123/1465 A conducting state.This causes the interruption of a cur- 51 Int. c1. F02p 3/02 rem flowingthrough an ignition to generate. an 1% [58] Field of Search 123/148 Enitio" voltage across the monostable multivibrator a capacitor isserially connected to a resistor high [56] References Cited in magnitudeof resistance to increase a time constant UNITED STATES PATENTS forcharging and a semiconductor diode is connected across the resistor todecrease at time constant for dis- 3,357,416 12/1967 Huntzinger 123/148E charging 3,605,713 9/1971 Le Masters... 123/148 E 3,322,107 5/1967Mieras 123/148 E 4 Claims, 2 Drawing Figures IGNITION TIME- DETECTIONCIRCUIT SWITCHING CIRCUIT MM IC I I I I I IGNITION CIRCUIT PATENTED FEBI 2 I974 FIG.

0 SPEED OF ROTATION OF ENGINE IGNITION TIME- SWITCHING CIRCUIT IGNITIONCIRCUIT DETECTION CIRCUIT IGNITION SYSTEM FOR INTERNAL COMBUSTION ENGINEBACKGROUND OF THE INVENTION This invention relates to an ignition systemfor use with an internal combustion engine including a semiconductorswitch adapted to be put in its nonconducting state to interrupt acurrent flowing through an ignition coil involved thereby to induce anignition voltage across the secondary of the coil each time the engineis to be ignited. More particularly it concerns improvements in such anignition system further including a monostable multivibrator for shapinga waveform of an ignition signal for controlling the semiconductorswitch.

In the conventional type of ignition systems for internal combustionengines, a time interval for which a current flowing through theignition coil is interrupted has remains unchanged independently of avariation in speed of rotation of the engine. This is because theinterrupting time interval for the ignition coil has been determined bythe operating time of the monostable multivibrator for which it is putin its semistable state. On the other hand, the ignition coil has beendesigned to have flowing therethrough 'a current for a time intervallong enough to permit ignition voltage or sparks produced thereby to besufficiently high or strong even in the case the engine increases inspeed of rotation to proportionally decrease a time interval between thesuccessive ignition sparks or an interspark time. Therefore the ignitioncoil has been energized through a supply circuit having a time constantin the low speed mode of operation equal to that in the high speed modeof operation of the engine. Accordingly, in the low. speed mode ofoperation the current continues to flow through the ignition coil aftera sufficiently high quantity of electromagnetic energy has beenaccumulated by the ignition coil. This has resulted in the generation ofheat on the ignition coil due to its electric resistance and thereforein an increase in temperature of the coil. Thus the ignition coil mightdecrease in useful life causing a decrease in reliability of theassociated ignition circuit.

SUMMARY OF THE INVENTION Accordingly it is an object of the invention toeliminate the abovementioned disadvantages of the conventional ignitionsystems for internal combustion engines.

The invention accomplishes this object by the provision of an ignitionsystem for use with an internal combustion engine comprising meansincluding an ignition time-detection circuit responsive to therotational movement of the engine to generate one first signal orignition signal each time the engine is to be ignited, a switchingcircuit triggered into one state or its operating state with theignitionsignal, the switching circuit including means for determining theoperating time thereof including a capacitor, and an ignition circuitresponsive to the triggering of the switching circuit into its operatingstate to interrupt a current flowing therethrough to produce an ignitionspark, characterized in that means is provided for changing an electriccharge on the capacitor in accordance with the speed of rotation of theengine.

The switching circuit may be formed preferably of a monostablemultibivrator including a pair of first and second semiconductorelements, the capacitor capable of charging when the first semiconductorelement is in its operating state, and a resistor high in magnitude ofresistance and connected in a charging circuit for the capacitor.

In order to discharge the capacitor of a minimum time constant when thesecond semiconductor element is in its operating state, a rectifierelement may be connected in a discharging circuit for the capacitor andacross the resistor connected in the charging circuit for the capacitor,the rectifier element being so poled as to be forward with respect to aflow of discharging current from the capacitor and when conducted,short-- circuiting the resistor.

BRIEF DESCRIPTION OF THE DRAWING The invention will become more readilyapparent from the following detailed description taken in conjunctionwith the accompanying drawing in which:

FIG. 1 is a graph useful in explaining the principles of the invention;and

FIG. 2 is a schematic circuit diagram of an ignition system constructedin accordance with the principles of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 of thedrawing, there is illustrated a graph useful in explaining theprinciples of the invention. In FIG. 1, wherein the axis of ordinatesrepresents time in an arbitrary unit and the axis of abscissasrepresents a speed of rotation of an-internal combustion engine in anarbitrary unit, a straight line A depicts the ignition characteristic ofthe conventional type of engines that a time interval between successiveignition sparks or an interspark time interval gradually decreases withan increase in speed of rotation of the engine. Another straight line Cshows an operating time of a monostable multivibrator used in aconventional ignition system such as above outlined. That is theoperating time of the monostable 'multivibrator for which it is in itssemistable state remains substantially unchanged in spite of an increasein speed of rotation of the engine. Since the monostable multivibratoris put in its operating state to open the associated semiconductorswitch as above described, a current flowing through the ignition coilis kept interrupted for the operating time of the monostablemultivibrator. In other words, the ignition coil has a currentinterrupting time equal to the operating time of the monostablemultivibrator and remaining substantially unchanged regardless of achange in speed of rotation of the engine.

Therefore, for the particular speed of rotation of the engine, a timeinterval for which. a current is flowing through the ignition coil orthe conduction time thereof is equal to a difference in ordinate betweenthe respective points on the lines A and C corresponding to that speedof rotation of the engine. It has been commonly practiced to render thisconduction time long enough to permit sufficiently strong ignition sparkto be produced even at the high speed mode of operation of the engine.Therefore the ignition coil has been energized through a'supply circuithaving a time constant remaining unchanged between the high and lowspeed modes of operation of the engine with the result that in the lowspeed mode of operation the current continues to flow through theignition coil even after a sufficiently high 3 quantity ofelectromagnetic energy has accumulated by the coil. This has led to thegeneration of heat on the ignition coil due to its electric resistanceand therefore to an increase in temperature of the coil. Therefore theignition coil might decrease in useful life while the associatedignition system might have a less reliability.

The invention contemplates to eliminate the disadvantages of the priorart type ignition systems as above described by the provision ofimproved means for rendering a time interval for which the currentflowing through the ignition coil is interrupted, longer in the lowspeed mode of operation of the associated internal combustion engine andrendering it shorter as the speed of rotation of the engine becomeshigher. Namely, as shown at straight line B in FIG. 1, the interruptingtime for the ignition coil is caused to change in proportion to avariation in interspark time relative to a change in speed of rotationof the engine as shown at line A in the same Figure. Thus, in the highand low speed modes of operation of the engine the ignition coil isgiven a sufficiently high quantity of electromagnetic energy whileeliminating a thermal loss of the ignition coil.

Referring now to FIG. 2, there is illustrated an ignition system for aninternal combustion engine constructed in accordance with the principlesof the invention. The arrangement illustrated means comprising anignition time-detection circuit ID for detecting time points at whichthe associated internal combustion en gine (not shown) is to be ignited,a transistor switching circuit MM and an ignition circuit IC. Theignition detection circuit ID includes a signal generator of theconventional construction responsive to the rotational movement of theengine to produce one ignition signal at each ignition time-point asemiconductor diode 12 and an NPN type transistor 14- disposed in seriescircuit relationship in the named order. The transistor 14 has a baseelectrode connected to the cathode electrode of the diode 12, an emitterelectrode connected to ground and a collector electrode connectedthrough a collector resistor 16 to a positive terminal of a source ofdirect current B with the generator also connected to ground. Thecollector electrode of the transistor 14 is connected to a capacitor 18which is, in turn, con nected to both an anode electrode of asemiconductor diode 20 and a cathode electrode of another semiconductordiode 22. The diode 20 is connected at the cathode electrode to groundand the diode 22 is connected at the anode electrode to the transistorswitching circuit MM.

The transistor switching circuit MM is formed of a monostablemultivibrator including an NPN type transistor 2 3 of common emitterconfiguration having a collector electrode connected to the positiveterminal of the source 8 through a collector resistor 26 and a baseelectrode connected to the anode electrode of the diode 22 and also toground through a resistor 28. The collector electrode of the transistor24 is further connected through a resistor 30 to a base electrode ofanother NPN type transistor 32 of common emitter configuration. Thetransistor 32 has a collector electrode connected to the base electrodeof the transistor 24 through a series combination of a capacitor 34 anda resistor 36 and also to the positive terminal of the source B througha collector resistor 38. The junction of the capacitor 34 and the baseelectrode of the transistor 24 is connected to the positive terminal ofthe source B through a resistor 40 and the resistor 36 is connectedacross a rectifier a semiconductor diode 42 so poled as to be permit adischarging current from the capacitor 34 to flow therethrough.

The ignition circuit IC includes an NPN type transistor 44, of commonemitter configuration having a base electrode connected to the collectorelectrode of the transistor 32 and a collector electrode connected toground through a constant voltage diode 46 such as a Zener diode andalso to the positive terminal of the source B through a primary windingof an ignition coil 48 having a secondary winding operatively coupled tothe associated engine (not shown) in the well known manner. 1

It is assumed that, the switching circuit or the monostablemultivibrator circuit MM is in its stable state in which the transistor24 is conducting while the transistor 32 is not conducting and that abase current is applied to the switching transistor 44 from the source Bthrough the resistor 38 to put it in the conducting state thereby topermit a current to flow through the primary winding of the coil 48 fromthe source B. Under the assumed condition, the capacitor 18 of theignition detection circuit ID has been charged from the source B throughthe resistor 16 and the diode 20 with the polarity illustrated in FIG.2.

If a time point where the engine (not shown) is to be ignited is reachedthe signal generator 10 produces a voltage indicative of an ignitionsignal. This voltage is then applied through the diode 12 to thetransistor 14 to put it in its conducting state. Therefore the capacitor18 charged with the illustrated polarity discharges through a circuittraced from the capacitor 18 through the nonconducting transistor 14,ground, the resistor 28 and the diode 22. This discharge of thecapacitor 18 causes the monostable multivibrator circuit MM to pass intoits semistable state or its operating state where it remains for a giventime interval before returning back to its original stable state. In thesemistable state of the monostable multivibrator circuit MM thetransistor 24 becomes nonconducting through the interruption of its basecurrent while the transistor 32 is put in its conducting state.

The conduction of the transistor 32 develops a second signal orswitching signal that causes the base current to the switchingtransistor 44 to be interrupted thereby to put the transistor 44 in itsnonconducting state. Thus the primary current flowing through theignition coil 48 is interrupted resulting in the generation of a highvoltage on the secondary of the coil 48 sufficient to apply an ignitionspark to the engine.

As well known, the monostable multivibrator circuit MM remains in itssemistable or operating state until the capacitor 34 has been completelydischarged. Therefore as long as the monostable multivibrator circuit MMis maintained in its operating state the transistor 44 is in itsnonconducting state in which the current is prevented from flowingthrough the ignition coil.

The invention includes means for controlling the discharging time of thecapacitor 34 in accordance with the speed of rotation of the associatedengine, the dis charging time determining the operating time of themonostable multivibrator MM for which it remains in its semistablestate. More specifically, the resistor 36 is preselected to be high inmagnitude of resistance and serially connected, in addition to thecollector resistor 38 for the transistor 32, to the capacitor 34 toimpart a large time constant to a circuit for charging the capacitor 34and also connected across the diode 42 poled to so as to permitdischarging current from the capacitor 34 to flow therethrough. Thismeasure is effective for decreasing an electric charge on the capacitor34 in the high speed mode of operation of the engine where theinter-spark time is short and also for decreasing ,the discharging timeof the capacitor 34 by means of the diode 42 conducting to shortcircuitthe resistor 36.

It is therefore appreciated that in the low speed mode of operation theelectric charge on the capacitor increases to lengthen the operatingtime of the monostable multivibrator for which it remains in itssemistable state whereas an increase in speed of rotation of the engineis accompanied by a gradually decrease in interspark time and thereforea decrease in electric charge on the capacitor resulting in a gradualdecrease in discharging time thereof.

In this way, the ignition system for internal combustion engines hasbeen provided having the desired characteristics that a current flowingthrough the ignition coil has its interrupting timelonger by the lowspeed mode of operation of the engine and shorter with an increase inspeed of rotation of the engine as determined by the operating time ofthe associated monostable multivibrator. In other words, the currentflowing through the ignition coil is interrupted for a time inter. valshorter in proportion to an increase in speed of rotation of the engineas shown at line B in FIG. 1.

The invention has several advantages. For example, even with the currentconducting time of the ignition coil determined so as to producesufficiently strong ignition sparks in the high speed mode of operationof the engine, the current conducting time thereof in the low speed modeof operation can be fixed to a minimum possible limit. Also the currentis permitted to flow through the ignition coil only for a predeterminedfixed time interval regardless of the speed of rotation of theassociated engine. Therefore the thermal loss due to the ignition coilcan reduce to a minimum necessary magnitude.

While the invention has been illustrated and described in conjunctionwith a single preferred embodiment thereof, it is to be understood thatvarious changes and modifications may be resorted to without departingfrom the spirit and scope of the invention. For example, the NPN typetransistor illustrated may be replaced by a PNP type transistor.

What is claimed is:

1. An ignition system for use with an internal combustion enginecomprising: ignition time-detection means for developing in use ignitionsignals corresponding to the ignition timing of anintemal combustionengine varying in time in dependence upon the speed of rotation of saidengine; a switching circuit receptive of said ignition signals andhaving two states and comprising means responsive to said ignitionsignals for switching into one state for a predetermined time for eachignition signal inversely proportional to the frequency of said ignitionsignals and means for developing switching signals corresponding infrequency and duration to said one state; and an ignition circuitreceptive of said switching signals for developing spark signals fordeveloping ignition sparks said spark signals corresponding in frequencyand duration to said switching signals; wherein said switching circuitcomprises a monostable multivibrator including a pair of first andsecond semiconductor elements, each having an operating state, achargeable and dischargeable capacitor being dischargeable when saidsecond semiconductor element is in said operating state, means defininga capacitor charging circuit connected to said capacitor including aresistor, and means defining a capacitor discharging circuit connectedto said capacitor including a semiconductor rectifier element connectedacross said resistor, said rectifier element being so poled as to beconductive with respect to a flow of discharging current from saidcapacitor and when conduc- -tive, shortcircuiting said resistor.

2. An ignition system for use with an internal combustion enginecomprising; ignition time-detection means for developing in use ignitionsignals corresponding to the ignition timing of an internal combustionengine varying in time in dependence upon the speed of rotation of saidengine; a switching circuit receptive of said ignition signals andhaving two states and comprising means responsive to said ignitionsignals for switching into one state for a predetermined time for eachignition signal inversely proportional to the frequency of said ignitionsignals and means for developing switching signals corresponding infrequency and duration to said one state; and an ignition circuitreceptive of said switching signals for developing spark signals fordeveloping. ignition sparks, said spark signals corresponding infrequency and duration to said switching signals; wherein said switchingcircuit comprises a monostable multivibrator including a pair of firstand second semiconductor elements, each having an operating state, atriggering circuit for triggering said first semiconductor element, achargeable and dischargeable capacitor being dischargeable when saidsecond semiconductor element is in said operating state, means defininga charging circuit connected to said capacitor including a resistor, andmeans defining a discharging circuit connected to said capacitorincluding a semiconductor rectifier element connected across saidresistor, said rectifier element being so poled as to be conductive withrespect to a flow of discharging current from said capacitor and whenconductive, shortcircuiting said resistor, and wherein said ignitiontime-detection means includes a signal generator responsive to therotational movementof the engine for generatingsaid ignition signal, athird semiconductor element having an inoperative state and an operatingstate responsive to said ignition signal from said signal generator,another'chargeable and dischargeable capacitor charged when said thirdsemiconductor element is in said inoperative state and dischargedthrough said semiconductor element when it is in said operating state, afirst semiconductor rectifier element poled forwardly with respect tothe polarity with which said another capacitor is charged, and a secondsemiconductor rectifier element poled reversely with respect to saidpolarity of said another capacitor and connected to said triggeringcircuit for said first semiconductor element included in said monostablemultivibrator.

3. An ignition system for use with an internal combustion enginecomprising: means for developing in use first signals corresponding tothe ignition timing of an internal combustion engine varying infrequency in dependence upon the speed of rotation of said engine; aswitching circuit receptive of said first signals and having two statesand comprising means responsive to said first signals for switching intoone state for each first signal for a variable duration of timedeterminable by the frequency of said first signals, and means fordeveloping second signals corresponding in frequency and duration tosaid one state thereby having a frequency corresponding to the frequencyof said first signals; an ignition circuit receptive of said secondsignals for developing engine ignition signals corresponding infrequency and duration to said second signals;

wherein said switching circuit comprises; a monostable multivibratorhaving means therein defining each variable duration of time comprisinga chargeable and dischargeable capacitor, voltage supply means having apredetermined voltage and for developing a voltage charge across saidcapacitor in the other state, means defining a capacitor charge pathconnected to said capacitor and receptive of said predetermined voltagefor charging said capacitor in said other state and having a first timeconstant, and means defining a capacitor discharge path connected tosaid capacitor for discharging same in said one state and having asecond time constant wherein said first time constant is substantiallygreater than said second time constant, whereby as said speed ofrotation of said engine increases the time for charging said capacitordecreases decresing the peak voltage charge across said capacitorthereby decreasing the time for discharging same;

and wherein said means defining said charge path and said means definingsaid discharge path comprise common circuit elements including; aresistor, and a rectifier element connected in parallel with saidresistor and poled to be in a nonconductive state during the charging ofsaid capacitor and in a conductive state during the discharge of saidcapacitor thereby shortcircuiting said resistor.

4. An ignition system according to claim 3, wherein said rectifierelement comprises a semiconductor diode.

1. An ignition system for use with an internal combustion enginecomprising: ignition time-detection means for developing in use ignitionsignals corresponding to the ignition timing of an internal combustionengine varying in time in dependence upon the speed of rotation of saidengine; a switching circuit receptive of said ignition signals andhaving two states and comprising means responsive to said ignitionsignals for switching into one state for a predetermined time for eachignition signal inversely proportional to the frequency of said ignitionsignals and means for developing switching signals corresponding infrequency and duration to said one state; and an ignition circuitreceptive of said switching signals for developing spark signals fordeveloping ignition sparks said spark signals corresponding in frequencyand duration to said switching signals; wherein said switching circuitcomprises a monostable multivibrator including a pair of first andsecond semiconductor elements, each having an operating state, achargeable and dischargeable capacitor being dischargeable when saidsecond semiconductor element is in said operating state, means defininga capacitor charging circuit connected to said capacitor including aresistor, and means defining a capacitor discharging circuit connectedto said capacitor including a semiconductor rectifier element connectedacross said resistor, said rectifier element being so poled as to beconductive with respect to a flow of discharging current from saidcapacitor and when conductive, shortcircuiting said resistor.
 2. Anignition system for use with an internal combustion engine comprising;ignition time-detection means for developing in use ignition signalscorresponding to the ignition timing of an internal combustion enginevarying in time in dependence upon the speed of rotation of said engine;a switching circuit receptive of said ignition signals and having twostates and comprising means responsive to said ignition signals forswitching into one state for a predetermined time for each ignitionsignal inversely proportional to the frequency of said ignition signalsand means for developing switching signals corresponding in frequencyand duration to said one state; and an ignition circuit receptive ofsaid switching signals for developing spark signals for developingignition sparks, said spark signals corresponding in frequency andduration to said switching signals; wherein said switching circuitcomprises a monostable multivibrator including a pair of first andsecond semiconductor elements, each having an Operating state, atriggering circuit for triggering said first semiconductor element, achargeable and dischargeable capacitor being dischargeable when saidsecond semiconductor element is in said operating state, means defininga charging circuit connected to said capacitor including a resistor, andmeans defining a discharging circuit connected to said capacitorincluding a semiconductor rectifier element connected across saidresistor, said rectifier element being so poled as to be conductive withrespect to a flow of discharging current from said capacitor and whenconductive, shortcircuiting said resistor, and wherein said ignitiontime-detection means includes a signal generator responsive to therotational movement of the engine for generating said ignition signal, athird semiconductor element having an inoperative state and an operatingstate responsive to said ignition signal from said signal generator,another chargeable and dischargeable capacitor charged when said thirdsemiconductor element is in said inoperative state and dischargedthrough said semiconductor element when it is in said operating state, afirst semiconductor rectifier element poled forwardly with respect tothe polarity with which said another capacitor is charged, and a secondsemiconductor rectifier element poled reversely with respect to saidpolarity of said another capacitor and connected to said triggeringcircuit for said first semiconductor element included in said monostablemultivibrator.
 3. An ignition system for use with an internal combustionengine comprising: means for developing in use first signalscorresponding to the ignition timing of an internal combustion enginevarying in frequency in dependence upon the speed of rotation of saidengine; a switching circuit receptive of said first signals and havingtwo states and comprising means responsive to said first signals forswitching into one state for each first signal for a variable durationof time determinable by the frequency of said first signals, and meansfor developing second signals corresponding in frequency and duration tosaid one state thereby having a frequency corresponding to the frequencyof said first signals; an ignition circuit receptive of said secondsignals for developing engine ignition signals corresponding infrequency and duration to said second signals; wherein said switchingcircuit comprises; a monostable multivibrator having means thereindefining each variable duration of time comprising a chargeable anddischargeable capacitor, voltage supply means having a predeterminedvoltage and for developing a voltage charge across said capacitor in theother state, means defining a capacitor charge path connected to saidcapacitor and receptive of said predetermined voltage for charging saidcapacitor in said other state and having a first time constant, andmeans defining a capacitor discharge path connected to said capacitorfor discharging same in said one state and having a second time constantwherein said first time constant is substantially greater than saidsecond time constant, whereby as said speed of rotation of said engineincreases the time for charging said capacitor decreases decresing thepeak voltage charge across said capacitor thereby decreasing the timefor discharging same; and wherein said means defining said charge pathand said means defining said discharge path comprise common circuitelements including; a resistor, and a rectifier element connected inparallel with said resistor and poled to be in a non-conductive stateduring the charging of said capacitor and in a conductive state duringthe discharge of said capacitor thereby shortcircuiting said resistor.4. An ignition system according to claim 3, wherein said rectifierelement comprises a semiconductor diode.